Sand discharge devices for rail vehicles have been known for a long time. As a rule, such a sand discharge device has a discharge unit and a storage container, which is filled with sand, and from which the sand is fed onto the rail to the wheels of the rail vehicle in various ways in order to improve the traction of the rail vehicle when accelerating and braking.
Within the framework of this disclosure, the term “sand” equally describes the quartz sand which is normally used and also other alternative sand-like media (granular materials) for increasing the friction between wheel and rail, such as metal oxides for example. Accordingly, within the framework of this disclosure, the term sand discharge device is also used for those devices which discharge the said alternative gritting materials.
In a widely used variant, the lower region of the storage container is designed in the form of a funnel. By means of a suction or pressure nozzle insert which is arranged at the bottom of the funnel-shaped region and acts as a discharge unit and is usually operated by compressed air, the sand is sucked out of the storage container and transported through sand feed pipes to in front of the wheels of the rail vehicle.
For various reasons, blockages of the sand feed pipes can occur during operation of the sand discharge device, for example due to the effect of moisture on a residual quantity of sand which has remained in the sand feed pipe from an earlier sanding operation, which can lead to agglutination or even freezing of the sand in the sand feed pipe.
It is therefore necessary for the sand feed pipe to be emptied from time to time by blowing air through it, that is to say compressed air only without the addition of sand. There is a range of solutions for this, which, however, predominantly try to prevent sand from being sucked from the storage container by means of moving parts so as to be able to blow the sand feed pipes free with compressed air only. However, if such devices are used for extended periods, these moving parts can become jammed by the sand thus resulting in operational faults and leaks.
When alternative gritting materials such as metal oxides are used, operational faults can occur with sand discharge devices according to the prior art: metal oxides have a higher weight than quartz sand, for example, therefore a greater quantity of air or a higher air pressure is required for sanding, which, with known devices, is only achieved with difficulty.